Cannot create a typescript valid nesting group

[tomasfrancisco]

I've been trying to find a good way to nest groups using @terrazzo/tokens-tools, but typescript (v5.6.3) seems to not be happy with it.

Reproduction @ CodeSandbox

Here are some references I've came across:

1. https://stackoverflow.com/questions/59896317/typescript-key-index-signature-only-for-all-properties-that-are-not-defined
2. Need way to express hybrid types that are indexable for a subset of properties  microsoft/TypeScript#17867

One workaround that could possible be used here is the repetition of type GroupCore in the inner properties and as an isolated union element of type Group.

Before:

export type Group = GroupCore & {
    [key: string]: GroupOrToken;
};

Workaround:

export type Group = GroupCore & {
    [key: string]: GroupOrToken | GroupCore;
} | GroupCore;

Or is there something I'm missing here?

[drwpow]

Ah you’re right this may be an impossible intersection. I actually think we could just have GroupCore | { [key: string]: GroupOrToken | GroupCore } to simplify it, since unions in TypeScript aren’t exclusive (often times they end up working the same as intersections for this reason). But if that doesn’t work, your fix is good!

This typing is more for internal usage, but complexity like this are why typing the DTCG spec with JSONSchema is tricky!